ارزيابي تحمل به يخ‌زدگي اكوتيپ‌هاي بارهنگ سرنيزه‌اي (Plantago lanceolata L.) در شرايط كنترل‌شده

Evaluation of Freeze Tolerance in Lancelot Plantain (Plantago lanceolata L.) Ecotypes under Controlled Conditions

به‌منظور بررسی تحمل به یخ‌زدگی بارهنگ سرنیزه‌ای، آزمایشی به‌صورت فاكتوریل در قالب طرح كاملاً تصادفی با سه تكرار در دانشكده كشاورزی دانشگاه فردوسی مشهد انجام شد. پنج اكوتیپ بارهنگ (بجنورد، كلات، مشهد، قاین و بیرجند) پس از سه ماه رشد و خوسرمایی در شرایط طبیعی در معرض هشت دمای یخ‌زدگی (صفر، 3-، 6-، 9-، 12-، 15-، 18- و 21- درجه سانتی‌گراد) قرار گرفتند. سپس گیاهان برای بازیافت به محیط گلخانه منتقل شدند. یك ماه بعد، بقاء و برخی از خصوصیات رشدی گیاهان با اندازه‌گیری صفاتی چون درصد بقاء، دمای پنجاه درصد كشندگی براساس درصد بقاء (LT50su)، تعداد برگ، سطح برگ، وزن خشك برگ و دمای كاهنده 50 درصد وزن خشك (RDMT50) مورد ارزیابی قرار گرفت. نتایج نشان داد كه درصد بقای اكوتیپ مشهد بیشتر از چهار اكوتیپ دیگر و LT50su آن نیز 3/5 درجه سانتی‌گراد از اكوتیپ بیرجند كمتر بود. اثر متقابل اكوتیپ و دما بر درصد بقاء معنی‌دار بود و تنها اكوتیپ‌های مشهد و بجنورد در دمای 15- درجه سانتی‌گراد بقاء داشتند. با كاهش دما به كمتر از 12- درجه سانتی‌گراد، تعداد و سطح برگ گیاهان كاهش یافت. همچنین كاهش دما به كمتر از 6- درجه سانتی‌گراد وزن خشك گیاهان را به‌طور معنی‌داری كاهش داد. براساس شاخص RDMT50 اكوتیپ بجنورد متحمل‌ترین و اكوتیپ بیرجند حساس‌ترین اكوتیپ بودند. بین درصد بقاء، دمای پنجاه درصد كشندگی براساس درصد بقاء و RDMT50 همبستگی منفی و معنی‌داری (به‌ترتیب***97/0- =r و *53/0- =r) وجود داشت.

Introduction Lancelot Plantain (Ribwort, narrow-leaf or English plantain) is a deep-rooted, short-lived perennial herb from Plantaginaceae family which has been used for various medicinal purposes for centuries, especially in Europe and only more recently has been proposed as a forage plant. The leaf of plantain is highly palatable for grazing animals, providing mineral-rich forage. Recently two productive upright cultivars of plantain have been bred and introduced, Grasslands Lancelot and the more erect winter active Ceres Tonic. Plantain grows moderately in winter but its main growth periods beings in spring and autumn with opportunistic summer growth. Although it reveals suitable winter survival in natural conditions, but there is not a lot of information about cold tolerance of this plant. So it is important to recognize the freeze tolerance of narrow leaf plantain for successful planting and utilization in cold regions such as Mashhad in Khorasan Razavi Province (Northeast of Iran). Determining LT50 point or critical temperature for survival of plant is the most reliable and simple method for evaluating cold tolerance of plants. Another reliable method for freeze tolerance of plants is estimation of temperature at which 50 % of dry matter reduces (RDMT50). This experiment was carried out to evaluate freeze tolerance of five ecotypes of Lancelot plantain according to the LT50su and RDMT50 indices. Materials and Methods In order to evaluate freeze tolerance of Lancelot plantain, a factorial experiment based on completely randomized design with three replications was carried out under controlled conditions at college of agriculture, Ferdowsi University of Mashhad. Five ecotypes of Lancelot plantain (Bojnourd, Kalat, Mashhad, Ghayen and Birjand) after three months growth and hardening in natural environment were transferred to a Thermo gradient freezer on January 20th, 2012 and exposed to eight freezing temperatures (Zero, -3, -6, -9, -12, -15, -18 and -21°C). The initial temperature of programmable freezer was 5°C; but gradually decreased in a rate of 2°C.h-1 until reach to desired temperatures. When the temperature reached to -2°C, the plants were sprayed with the Ice Nucleation Active Bacteria (INAB) to help the formation of ice nuclei in them. Then for recovery, plants were transferred to greenhouse and after one month, survival and growth traits of plants were determined by measuring characteristics such as survival percentage (Su%), the lethal temperature for 50% of plants according to the survival percentage (LT50su), number of leaf, leaf area, leaf dry weight and temperature at which 50% of dry matter reduces (RDMT50). LT50su and RDMT50 were determined after plotting survival percentage and dry weight data curves versus experimental temperatures respectively. Analysis of variance performed by MSTAT-C software and correlation between data carried out by MINITAB 15 program. Mean separation was conducted by least significant difference (LSD) test at 1% probability level. Results and Discussion Analysis of variance showed significant difference between plantain ecotypes and freezing temperatures for survival %. Means comparison showed that survival percentage of Mashhad ecotype was more than other ecotypes. Interaction effects of ecotype and temperature on survival percentage was significant too and only Mashhad and Bojnourd ecotypes in -15°C were alive. Evaluating the temperature-survival curve allowed estimation of a LT50 value, similar to the LD50 (lethal dose for 50% of the subjects) in a toxicity screen. In this experiment there was significant difference between ecotypes at the point of this indicator view and LT50su of Mashhad ecotype was 5.3°C lower than Birjand ecotype. With decreasing the temperature to less than -12°C, number of leaf and leaf area were decreased. In addition decreasing of temperature to less than -6°C, reduced dry weight of plants noticeably. Mashhad and Birjand ecotypes produced the most and the least leaf number and leaf dry weight but Kalat and Birjand ecotypes produced the most and the least leaf area respectively after the recovery period. Based on RDMT50 index, Bojnourd ecotype was the most tolerant and Birjand ecotype was the most sensitive ecotype. There was high and negative correlation between Survival percentage, LT50su and RDMT50 (r= -0.97*** and r= -0.53* respectively) which confirmed that these indices were suitable alternatives for each other in estimating the freeze tolerance of narrow leaf plantain. Conclusions Based on these results, Lancelot plantain has the ability to withstand winters which are not colder than -16 °C. Despite this for better perception of Plantain freeze tolerance potential, more experiments under controlled and field conditions are required.